Coffee's Surprising Body Composition and Hormone Link

Key takeaways

• In a Finnish study of 2,264 adults around age 46, people who drank more coffee tended to have less total and abdominal fat and more skeletal muscle, even when their BMI was similar to lighter coffee drinkers.
• Higher coffee intake tracked with lower levels of certain amino acids linked to less favorable blood sugar handling, along with a more favorable glucose-insulin profile in men.
• Coffee drinkers also showed a distinct hormonal signature — higher testosterone and SHBG in men, higher SHBG and lower free androgens in women — that held up even after accounting for BMI and lifestyle habits.

BMI has always been a blunt tool. It can't distinguish between someone carrying more muscle and someone carrying more fat, which is exactly where this study gets interesting. Researchers at the University of Oulu looked at 2,264 people from the Northern Finland Birth Cohort, all around 46 years old, and compared habitual coffee drinkers against those who drank less, using detailed measures of body fat, abdominal fat, and skeletal muscle rather than BMI alone.

Even when two people had a similar BMI, the ones who drank more coffee tended to carry less total fat, less abdominal fat specifically, and more skeletal muscle. That's a meaningfully different body composition hiding behind what would look like the same number on a scale, and it's the kind of detail that only shows up when researchers dig past a single, rough metric.

The amino acid clue

One of the more technical findings involves branched-chain amino acids, a group of building blocks found in protein that the body also uses as an energy source. Higher coffee intake was linked to lower circulating levels of these amino acids in both men and women. That's notable because elevated branched-chain amino acids have previously been tied to less favorable blood sugar handling over time.

In men specifically, greater coffee intake also lined up with a more favorable glucose-insulin profile — another piece of the metabolic puzzle suggesting coffee habits may be tangled up with how efficiently the body manages blood sugar, not just how much fat it stores.

A hormonal signature that surprised the researchers

Coffee's link to body composition wasn't the only unexpected pattern. The study also found distinct differences in sex hormones between coffee drinkers and non-drinkers, and the pattern looked different for men and women. In men, higher coffee intake tracked with higher total and bioavailable testosterone and higher sex hormone-binding globulin (SHBG) — a protein that regulates how much testosterone is freely available in the body — alongside modestly lower free testosterone. In women, higher intake was mainly linked to higher SHBG and lower measures of free androgens.

The lead researcher noted that this hormonal signature didn't disappear even after adjusting for BMI and lifestyle factors, which suggests it isn't simply explained away by coffee drinkers happening to be leaner or more active. Something about habitual coffee intake appears to be tangled up with hormone regulation in ways that differ by sex, an angle that hasn't been explored much until now.

Why this fits the bigger coffee story

Coffee has already been associated with favorable metabolic outcomes in prior research, and Finland is a useful place to study this given it's one of the highest coffee-consuming countries in the world, with an average intake of roughly 26 pounds per person per year. What this new study adds is a plausible biological thread connecting coffee to metabolism: hormonal pathways. Researchers don't yet know which specific compounds in coffee might be responsible, and they're now investigating that question using animal models, with the eventual goal of moving toward studies in people.

It's worth being clear-eyed about what this study can and can't say. It's observational, so it can show that coffee habits and these biological markers travel together, not that coffee itself is causing the changes. But it does add a coherent, mechanistic layer to what was previously more of an association.

The takeaway

This isn't a case for pouring more coffee to build muscle or shift hormones. It's a reminder that a habit many of us already have may be interacting with the body in more layered ways than "just caffeine and alertness." As the researchers work toward understanding which compounds are involved and whether the relationship holds up in intervention studies, this is one to keep an eye on rather than act on just yet.

References:

Luca Verroest, Jari Jokelainen, Shalini Choudhary, Jaroslaw Walkowiak, Toni Karhu, Saranya Palaniswamy, Juha Auvinen, Marjo-Riitta Jarvelin, Karl-Heinz Herzig, Ghulam Shere Raza. Associations of habitual coffee intake with testosterone and cardiometabolic markers: the Northern Finland Birth Cohort 1966 study. European Journal of Nutrition, 2026; 65 (5). DOI: 10.1007/s00394-026-04038-z